The present invention relates to a process for preparing a molded article from a mixture of an olefin resin and a hydrolyzed ethylene-vinyl acetate copolymer (hereinafter referred to as "EVOH"), and more particularly to a process for preparing a molded article having excellent long run processability during melt-molding and capable of giving molded articles having remarkably improved quality.
Various molded articles can be obtained by melt-molding mixtures of an olefin resin such as polyethylene or polypropylene and EVOH. Objects of the melt-molding are
(1) to provide molded articles having physical properties which cannot be obtained from use of only one of the olefin resin and EVOH, as discussed in, for instance, Japanese Examined Patent Publication No. 1032/1967 and No. 44579/1974, Japanese Unexamined Patent Publication Nos. 7038/1973, 65544/1975 and 122950/1983, and the like, or
(2) to reuse waste articles such as scraps or cut edges of the molded articles produced during laminating and inferior goods.
When melt-molding the mixture of the olefin resin and EVOH to give molded articles such as films and sheets, there are some problems that the mixture gells, and colored resins or carbonized resins, which are generated by occurrence of thermal decomposition, adhere to an inner wall of an extruder during melt-molding. As a result, melt-molding cannot be continuously conducted for a long period of time. In other words, so-called long run processability is poor. Also, since the gelled material is often incorporated into the molded article, the obtained molded articles are inferior in quality, for instance, fish eyes are generated on the film.
When reusing waste articles (scraps or cut edges of laminates, inferior goods, and so on) of the laminates of the olefin resin and EVOH, it is particularly important to solve the above-mentioned problems.
In fact, recently, there have been few cases where the olefin resin or EVOH is molded singly to give wrapping or packaging materials such as films, sheets, containers or bottles and there have been many cases where they are laminated, if necessary using an adhesive, to give multi-layer laminates of the olefin resin layer and the EVOH layer, since in the market the wrapping or packaging materials are required to have multi-function. In such a laminating, generally, a lot of waste articles such as scraps or cut edges of the laminates and inferior goods are generated. It is required to reuse of the waste articles in the art.
The long run processability is not very poor when EVOH or the olefin resin is molded singly, but it becomes remarkably poor when molding the olefin resin with EVOH even if using a slight amount of EVOH. In melt-molding of the mixture of the olefin resin and EVOH, screen meshes are very often choked with the gelled materials, or melted resins adhere to a screw in an extruder. At every times when the screen meshes are choked or the melted resins adhere to the screw, remarkable troublesome operations such that the extruder is disassembled than the screen and the screw are cleaned up are required.
In order to improve the long run processability in melt-molding of the mixture of olefin resin and EVOH and provide molded articles having excellent quality, Japanese Unexamined Patent Publications No. 15243/1987 and No. 179530/1987 have proposed that a hydrotalcite compound is added to the olefin resin and EVOH, then the mixture is molded. However, according to the process, there are problems that improvement of long run processability is insufficient, that is, melt-molding can be continuously carried out for about 10 days at most, a bad smell is given out during melt-molding, the molded articles are colored, and the like.
An object of the present invention is to provide a process for preparing a molded articles having good long run processability and capable of providing molded articles having remarkably improved quality.
This and other objects of the present invention will become apparent from the description thereof.